'fifty-dollar' is a compound of 'fifty' and 'dollar'. 'fifty' originates from Old English, specifically the word 'fīftig', where 'fīf' meant 'five' and '-tig' (tīġ) meant 'a group of ten'. 'dollar' originates from Low German, specifically the word 'taler', ultimately from 'Joachimsthaler' (a coin named after Joachimsthal).

'fifty' developed from Old English 'fīftig' into Middle and then Modern English 'fifty'. 'dollar' changed from the Low German word 'taler' (from 'Joachimsthaler') and entered English as 'dollar' in the Early Modern period, later becoming the general term for the currency unit.

Originally, 'dollar' referred to a particular silver coin (the taler/Joachimsthaler); over time it shifted to mean the standard unit of currency 'dollar'. Consequently, 'fifty-dollar' came to mean either a banknote worth fifty dollars or adjectivally 'costing fifty dollars'.